Abstract
The Mt. Kilimanjaro region is known for its long history of intensive agriculture, but the temporal extent of human activity and its impact on the regional ecosystem are not well known. In this study, climate-human-landscape interactions during the past ~2200 years were examined using climate and vegetation proxies extracted from the continuous and high-resolution sediment record of Lake Chala. Ancient-to-modern regional human activity is documented against a backdrop of long-term vegetation dynamics in the low-elevation savanna woodland southeast of Mt. Kilimanjaro and riparian forest within Chala crater. During prolonged dry periods (~1170–1300 CE), succulent dry crater forest expanded relative to the moist lakeshore forest. The savanna landscape surrounding Chala crater was relatively stable through time, except that savanna grasses were stimulated by higher precipitation, consistent with the fuel-limited fire regime evidenced in the charcoal record. Expansion of subalpine ericaceous vegetation and a general decline in Afromontane forest taxa on Mt. Kilimanjaro after 550 CE may reflect a lowering of its upper forest line. The earliest robust signature of human influence on regional vegetation involves an increase in ruderal (weedy) plant taxa around 1100 CE, possibly associated with the development of Chagga homegardens and associated agroforestry in the submontane forest zone. A first hint of cereal agriculture (likely sorghum) is observed around 1550 CE, followed by a more robust signature from 1780 CE onwards which likely reflects the start of lowland irrigation agriculture. From 1780 CE we also find the first undisputed appearance of maize, introduced to East Africa about a century earlier.
Highlights
The foothills and sub-montane forest zone of Mt
Kilimanjaro, between 1100 and 2100 m above sea level, have long been identified as an area of intensive agriculture in East Africa (Stump and Tagseth, 2009), with a long history of human occupation and farming surrounded by a ‘sea’ of lowland savanna relatively untouched by agricultural activity
Utilizing the plentiful water supply coming from higher up the mountain and an intricate irrigation scheme to distribute it effectively, the Chagga people inhabiting this region practice a traditional form of agroforestry which relies on the cultivation of banana, coffee and cereals in settlements known as homegardens
Summary
The foothills and sub-montane forest zone of Mt. Kilimanjaro, between 1100 and 2100 m above sea level (asl), have long been identified as an area of intensive agriculture in East Africa (Stump and Tagseth, 2009), with a long history of human occupation and farming surrounded by a ‘sea’ of lowland savanna relatively untouched by agricultural activity. Different pastoralist groups have inhabited or migrated through these lowlands over the centuries, undoubtedly it is the Chagga people who have had the most pronounced impact on the Mt. Kilimanjaro landscape (Stump and Tagseth, 2009). The Mt. Kilimanjaro irrigation scheme, which altogether consists of more than 1000 furrows with lengths of up to 30 km (Stump and Tagseth, 2009), allowed intensive agriculture by creating a safeguard against drought-related water shortages, and provided a means of support to large numbers of people. Kilimanjaro in previous centuries remains vague, with historians drawing their information from indigenous oral histories and accounts of early European travellers, but lacking the evidence required to bridge the gap between 19th century historical reports and earlier archaeological evidence (Stump and Tagseth, 2009)
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